The invention relates to a signal diversity receiving system for mobile reception of frequency modulated singals, comprising a receiver and a diversity processor, which receives the input signals and applies a different one of the input signals to the receiver when interference occurs on the signal currently being used.
Such an arrangement is, for example, known from the NTG-Fachberichte Band 72 (VDE Verlag), p. 241, picture 5b, as a scanning diversity combiner. In this case the diversity combiner selects one signal out of the two input signals offered, while that signal exceeds a specific predetermined voltage threshold Umin. Falling short of this level is considered by the combiner to be interference. The interference detector operates in a digital mode, and in the case of the combiner shown comprises a comparator having a threshold voltage At the output of the deletion signal is developed moving the switch into the other position.
Such a system has the disadvantage that when interference occurs as defined above, the switch is moved into the other position each time, regardless of the signal quality history of the signal applied to the signal input. For example, if the voltage at one of the two signal inputs has been essentially lower on average than the voltage at the other input over a long period of time, and then for a short period of time at the signal input with a larger signal on average the value falls below U.sub.min, a switching through to the input with the signal which is worse on average will take place, although most probably a still worse signal is available there. In such a case the system often switches back and forth between the signal inputs at a very high switching rate. This leads to an additional disturbing element in the system, and a consequent degradation of the quality of the signal switched through to the receiver. When utilizing diversity aerial selection there will be consequent disturbing noise in the clock rate at the switching frequency on reception, which is often considered to be switching noise.